Users of the popular PGP Desktop encryption tool are being urged to upgrade to the latest version of the software after the discovery of a flaw in the code.

The flaw exists in the Windows Service which PGP Desktop installs, and could be used by any local or remote user to run code with escalated privileges.

Vulnerability testers NGS Software rated the flaw as a 'medium risk' and said that it affects versions of the software earlier than PGP Desktop 9.5.1.

"The vulnerability occurs because the code responsible for processing the objects passed over the interface to the service does not perform any kind of validation on these objects," said Peter Winter-Smith of NGS Software.

"Instead it trusts that the object data is completely safe in the form that it is received, i.e. absolute pointers are trusted without validation."

NGS Software does not yet have a workaround and is urging all PGP Desktop users to upgrade as a matter of urgency.

"NGS Software reported this to us, and the actual problem is fixed in PGP 9.5.1 (released 2 November 2006) where the message is parsed correctly. In 9.5.2, there's an additional fix in which the message socket is explicitly opened for local-access only," said Jon Callas, chief technical officer of PGP Corporation

"This does not affect 9.0.x or any other previous version."